The beneficial effects, both therapeutic and cosmetic, of exposure of the body to sunlight are too well known to require elaboration.
Attempts to avail oneself of these beneficial effects, however, are frequently beset by difficulties, chief among which is the chilling effect of wind. Even on bright sunny days, when the air is warm, e.g. from passage over extensive areas of sun-heated land, the effect of wind may exert a chilling effect by hastening the rate of evaporation of perspiration, and by stirring up airborne dust and debris. On days when the sunlight is relatively weak, whether because of intervening clouds or haze or because of the angle of incidence of the sun's rays upon the surface of the earth (particularly during the cooler fall, winter and spring months), its warming effect is appreciably diminished, and even a slight movement of air may create a distinctly uncomfortable chill.
In order to illustrate the importance of effective collection of radiation to comfort, a series of readings were taken at various intervals on opposite sides, separated by about 35 feet, of the same building (i.e. the inventor's residence). The two sides selected were the shady (northwesterly) and the sunny (easterly--southeasterly) sides. The times of the readings, and the values observed, are set forth in the following Table:
______________________________________ Temp. .degree. F. Date Time NW SE ______________________________________ 2/27/74 1 PM 30 72 3/14/74 2 PM 38 82 4/7/74 1:30 PM 50 93 5/7/74 2 PM 49 81 (95.degree. F. on dark wool coat; better wind shelter and orientation) 5/8/74 Noon 54 100 7/8/74 Noon to 1:30 PM 79 111 (117 w/darker background and 120 w/15.degree. rotation towards W) 1/15/77 Noon 26 80 2/1/77 1 PM 19 56 (some wind) ______________________________________
Numerous expedients have been employed to permit exposure to solar radiation while ameliorating the cooling effect of air movement. Among these may be mentioned, for example, such devices as cabana chairs, beach umbrellas and the like (which may also be used for the opposite purpose, i.e. to protect the user from excessively intense or prolonged radiation), and plastic canopies or screens designed to shield the user from the wind, while allowing free access of radiation, or at least to that portion of the radiation to which the shield is transparent.
These expedients, while successful to a degree, cannot be completely effective because of the nature of air currents. When an air current encounters an obstacle of the type just described, it does not oridinarily split and pass around the obstacle in laminar flow fashion, at least unless the obstacle is aerodynamically engineered and properly oriented to achieve such laminar flow. Rather, it tends to create a partial vacuum on the side opposite to that against which the air current collides, and draws air in from the sides in swirling eddy currents, which are nearly as desirable as the primary air current from the viewpoint of comfort.